Laser bonded glass-silicon vapor cell

ABSTRACT

Various embodiments comprise a laser bonded glass-silicon vapor cell for performing spectroscopy on particles like atoms or molecules. In some examples, the laser bonded glass-silicon vapor cell comprises a glass base, a glass top, a silicon piece, and a filling material. The silicon piece comprises at least one through hole. The lower surface of the silicon piece is hermetically bonded to the glass base. The upper surface of the silicon piece is laser bonded to the glass top. The filling material is positioned in a cavity formed by the through hole, the glass base, and the glass top. The filling material may comprise an alkali metal, a salt slush, an inert gas, or a vacuum encapsulation.

RELATED APPLICATIONS

This patent application claims the benefit of and priority to U.S.Provisional Patent Application 63/227,742 entitled, “LASER WELDED GLASSSILICON VAPOR CELL FOR AN OPTICALLY PUMPED MAGNETOMETER” which was filedon Jul. 30, 2021, and which is hereby incorporated by reference in itsentirety into this patent application.

BACKGROUND

Glass vapor cells are devices configured to perform spectroscopy onatoms and molecules. Exemplary uses of glass vapor cells includeperforming magnetoencephalography to detect magnetic field generated byneuronal activity. Glass vapor cells comprise a glass capsule thathouses a filling material. Glass vapor cells are constructed by creatinga glass cavity and depositing a filling material like an alkali metalinto the glass cavity in an inert environment like a vacuum. The glasscavity is heated and pinched off to fully encapsulate the fillingmaterial within the glass cavity. Unfortunately, the glass vapor cellsare inefficient and difficult to construct. Moreover, the constructionprocess of glass vapor cells cannot be effectively and efficientlyscaled.

Other types of vapor cells for performing spectroscopy on atoms andmolecules comprise hybrid glass-silicon vapor cells. The glass-siliconvapor cells comprise a capsule that houses a filling material where thesilicon forms the walls of the capsule, and the glass forms the base andtop of the capsule. Glass-silicon vapor cells are constructed byanodically bonding the silicon to the glass to encapsulate the fillingmaterial like an alkali metal. The anodic bonding process used toconstruct the glass-silicon vapor cells inefficiently requires anelevated temperature. The elevated temperature results in undesiredchemical reactions that alter the chemical composition of the fillingmaterial. Moreover, the elevated temperature may cause the fillingmaterial to diffuse into the glass. The diffusion results in a decreaseof cell pressure and a change in the composition of the glass.Unfortunately, the anodic bonding process does not efficiently andeffectively construct glass-silicon vapor cells. Moreover, the decreasein cell pressure, altered composition of the glass, and undesiredchemical reactions may negatively impact the use of the glass-siliconvapor cell.

OVERVIEW

This Overview is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

Various embodiments of the present technology relate to solutions forthe manufacture and use of vapor cells for atomic spectroscopy. In someembodiments, a laser bonded glass-silicon vapor cell for performingspectroscopy on particles like atoms or molecules is disclosed. In someexamples, the laser bonded glass-silicon vapor cell comprises a glassbase, a glass top, a silicon piece, and a filling material. The siliconpiece comprises at least one through hole. The lower surface of thesilicon piece is hermetically bonded to the glass base. The uppersurface of the silicon piece is laser bonded to the glass top. Thefilling material is positioned in a cavity formed by the through hole,the glass base, and the glass top. The filling material may comprise analkali metal, a salt slush, an inert gas, or a vacuum encapsulation.

In some embodiments, a method of manufacturing a laser bondedglass-silicon vapor cell for performing spectroscopy on particles likeatoms or molecules is disclosed. The method comprises making a throughhole in a silicon piece. The method continues by hermetically bonding alower surface of the silicon piece to a glass base. The method continuesby positioning a filling material in the through hole of the siliconpiece on the glass base. The method continues by clamping a glass top tothe silicon piece to contact the glass top with an upper surface of thesilicon piece. The method continues by laser bonding the upper surfaceof the silicon piece to the glass top. The method continues by removingthe clamping.

DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout the several views.While several embodiments are described in connection with thesedrawings, the disclosure is not limited to the embodiments disclosedherein. On the contrary, the intent is to cover all alternatives,modifications, and equivalents.

FIG. 1 illustrates an example of a laser bonded glass-silicon vaporcell.

FIG. 2A illustrates an example of a laser bonded glass-silicon vaporcell.

FIG. 2B illustrates an example of a laser bonded glass-silicon vaporcell.

FIG. 3 illustrates an exemplary method of manufacture for a laser bondedglass-silicon vapor cell.

FIG. 4A illustrates an exemplary method of manufacture for a laserbonded glass-silicon vapor cell.

FIG. 4B illustrates an exemplary method of manufacture for a laserbonded glass-silicon vapor cell.

FIG. 4C illustrates an exemplary method of manufacture for a laserbonded glass-silicon vapor cell.

FIG. 4D illustrates an exemplary method of manufacture for a laserbonded glass-silicon vapor cell.

FIG. 5 illustrates an example of laser bonded glass-silicon vapor cells.

FIG. 6 illustrates an exemplary operational environment for a laserbonded glass-silicon vapor cell.

FIG. 7 illustrates an exemplary operational environment for a laserbonded glass-silicon vapor cell.

The drawings have not necessarily been drawn to scale. Similarly, somecomponents or operations may not be separated into different blocks orcombined into a single block for the purposes of discussion of some ofthe embodiments of the present technology. Moreover, while thetechnology is amendable to various modifications and alternative forms,specific embodiments have been shown by way of example in the drawingsand are described in detail below. The intention, however, is not tolimit the technology to the particular embodiments described. On thecontrary, the technology is intended to cover all modifications,equivalents, and alternatives falling within the scope of the technologyas defined by the appended claims.

DETAILED DESCRIPTION

The following description and associated figures teach the best mode ofthe invention. For the purpose of teaching inventive principles, someconventional aspects of the best mode may be simplified or omitted. Thefollowing claims specify the scope of the invention. Note that someaspects of the best mode may not fall within the scope of the inventionas specified by the claims. Thus, those skilled in the art willappreciate variations from the best mode that fall within the scope ofthe invention. Those skilled in the art will appreciate that thefeatures described below can be combined in various ways to formmultiple variations of the invention. As a result, the invention is notlimited to the specific examples described below, but only by the claimsand their equivalents.

Various embodiments of the present technology relate to laser bondedglass-silicon vapor cells. More specifically, embodiments of the presenttechnology relate to systems and methods for constructing laser bondedglass-silicon vapor cells for use in particle spectroscopy. Nowreferring to the Figures.

FIG. 1 illustrates two-dimensional cross section view of laser bondedglass-silicon vapor cell 100. Laser bonded glass-silicon vapor cell 100is a vapor cell configured to perform spectroscopy on atoms andmolecules. For example, laser bonded glass-silicon vapor cell 100 may beused to perform magnetoencephalography to detect and characterize amagnetic field generated by neuronal activity of a human brain. Laserbonded glass-silicon vapor cell 100 comprises glass base 101, siliconpiece 111, glass top 121, filling material 131, hermetic bond 141, laserbond 151, cell cavity 161, and cell walls 171. Silicon piece 111 maycomprise a portion of a silicon wafer. For example, silicon piece 111may be cut out of a silicon wafer to construct laser bondedglass-silicon vapor cell. In some examples, silicon piece 111 maycomprise an entire silicon wafer. Silicon piece 111 may be replaced by adifferent type of material that can hermetically bond to glass and thatdoes not react, mildly reacts, or undergoes a desired chemical reactionwith filling material 131. In this example, laser bonded glass-siliconvapor cell 100 comprises a rectangular shape, however the shape of vaporcell 100. Silicon piece 111 comprise a through hole that passes throughsilicon piece 111 to form cell walls 171. Cell walls 171 typically runperpendicular to the horizontal axis of silicon piece 111. For example,a drilling tool may bore entirely through silicon piece 111 to create athrough hole.

Silicon piece 111 is positioned between glass base 101 and glass top121. Glass base 101 and glass top 121 are transparent to laser light.Glass base 101 and glass top 121 may comprise low-thermal-expansionborosilicate glass, aluminosilicate glass, or another type of glass ortransparent material that can hermetically bond to silicon piece 111.Glass base 101 and glass top 121 are transparent to laser light. Forexample, laser bonded glass-silicon vapor cell 100 may be used in anOptically Pumped Magnetometer (OPM) and lasers light emitted from lasersin the OPM may pass through glass base 101 and glass top 121 to interactwith filling material 131. In some examples, glass base 101 and glasstop 121 may comprise an anti-reflective coating positioned on theirsurfaces. For example, anti-reflective coating may be positioned ontheir outer surfaces opposite their surfaces contacting silicon piece111. The anti-reflective coating inhibits laser light from reflectingoff of the surfaces of glass base 101 and glass top 121. Theanti-reflective coating may comprise aluminum oxide, titanium oxide, oranother type of anti-reflective material that forms a thin film layerdeposited on the outer surfaces of glass base 101 and glass top 121. Insome examples, glass base 101 and glass top 121 may be fully coated inthe anti-reflective coating. In some examples, the anti-reflectivecoating may be patterned and only partially cover glass base 101 andglass top 121.

The lower surface of silicon piece 111 is bonded to the upper surface ofglass base 101 by hermetic bond 141. Hermetic bond 141 may comprise ananodic bond, a laser bond, a hybrid anodic/laser bond, or some othertype of bond that hermetically binds silicon piece 111 to glass base101. The upper surface of silicon piece 111 is bonded to the lowersurface of glass top 121 by laser bond 151. For example, a laser may beapplied to glass top 121 and silicon piece 111 to create laser bond 151.Laser bond 151 may comprise two bond types. The first bond type maycomprise a laser weld where the upper surface of silicon piece and thelower surface of the glass top 121 melt into each other. The second bondtype may comprise a laser induced ion diffusion bond that hermeticallycontacts silicon piece 111 and glass top 151. In some examples, laserbond 151 comprises a hybrid anodic/laser bond. Glass base 101, glass top121, hermetic bond 141, laser bond 151, and cell walls 171 form ahermetic seal that encapsulates cell cavity 161. The exposed area ofglass base 101 and glass top 121 form windows that allow light to enterand pass-through cell cavity 161.

Filling material 131 is positioned on the upper surface of glass base101 within cell cavity 161. Filling material 131 may comprise an alkalimetal, alkali slush, a salt slush, an inert gas, a vacuum encapsulation,and/or some other type of filling material. The alkali metal maycomprise a metal like rubidium. The alkali slush may comprise an alkalisalt and azide mixture like rubidium azide. The alkali slush maycomprise an alkali azide like rubidium azide. The inert gas may comprisean inert like nitrogen or helium. The vacuum encapsulation may comprisea volume of low-pressure contained within cell cavity 161. It should beappreciated that the material type of filling material 131 depends inpart on the intended use for laser bonded glass-silicon vapor cell 100.For example, if laser bonded glass-silicon vapor cell 100 is used in anOPM, filling material 131 may comprise rubidium metal and an inert gas.When assembled, filling material 131 may partially or fully sublimateand fill cell cavity 161 with the sublimated vapors. For example,filling material 131 may comprise rubidium metal and the rubidium metalmay sublimate to fill cell cavity 161 with rubidium vapors.Advantageously, the laser bonded glass-silicon vapor cell 100 can beefficiently constructed. Moreover, the laser bonding processhermetically bonds glass top 121 to silicon piece 111 withoutexcessively heating laser bonded glass-silicon vapor cell 100 to anelevated temperature.

FIGS. 2A and 2B provide additional views of laser bonded glass-siliconvapor cell 100 illustrated in FIG. 1 . FIG. 2A illustrates a top-downview of laser bonded glass-silicon vapor cell 100. The top-down view oflaser bonded glass-silicon vapor cell 100 comprises silicon piece 111,glass top 121, filling material 131, laser bond 151, cell cavity 161,and cell walls 171. Glass top 121 is positioned above silicon piece 111.Laser bond 151 encircles cell walls 171 and hermetically binds the lowersurface of glass top 121 to the upper surface of silicon piece 111.

FIG. 2B illustrates a bottom-up view of laser bonded glass-silicon vaporcell 100. The bottom-up view of laser bonded glass-silicon vapor cell100 comprises glass base 101, silicon piece 111, filling material 131,hermetic bond 141, cell cavity 161, and cell walls 171. Glass base 101is positioned below silicon piece 111. Hermetic bond 141 encircles cellwalls 171 and hermetically binds the upper surface of glass base 101 tothe lower surface of silicon piece 111.

FIG. 3 illustrates process 300. Process 300 comprises a method ofmanufacturing a laser bonded glass-silicon vapor cell. For example,process 300 may be used to construct laser bonded glass-silicon vaporcell 100 illustrated in FIGS. 1, 2A, and 2B. The structure andoperations of process 300 may differ in other examples. The operationsof process 300 comprise making a through hole in a silicon piece (step301). The operations further comprise hermetically bonding the lowersurface of the silicon piece to a glass base (step 302). The operationsfurther comprise positioning a filling material in the through hole ofthe silicon piece on the glass base (step 303). The operations furthercomprise clamping a glass top to the silicon piece to contact the glasstop with the upper surface of the silicon piece (step 304). Theoperations further comprise laser bonding the upper surface of thesilicon piece to the glass top (step 305). The operations furthercomprise removing the clamping (step 306).

FIGS. 4A-4D illustrate process 400. Process 400 comprises a method ofmanufacturing a laser bonded glass-silicon vapor cell. For example,process 400 may be used to construct laser bonded glass-silicon vaporcell 100 illustrated in FIGS. 1, 2A, and 2B. Process 400 comprises anexample of process 300, however process 300 may differ. In otherexamples, process 400 may differ.

FIG. 4A illustrates process step 401. Process step 401 comprisesdrilling a silicon piece to create a through hole that transverses thehorizontal plane of the silicon piece. For example, a mechanical drillmay be lowered onto the silicon piece. The mechanical drill may beturned on and bore a through hole in the silicon piece. In someexamples, multiple through holes may be drilled in the silicon piece.The silicon piece is then positioned on a glass base. In some examples,the glass base is also drilled to create an indentation on the uppersurface of the glass base. The indentation may be configured to hold afilling material (e.g., filling material 131). In some examples, thesilicon piece may be further drilled to create an indentation in thesilicon piece alongside the through that is configured to hold a fillingmaterial. For example, the indentation in the silicon piece may be madeon the through hole walls to create a pocket to hold a filling material.

FIG. 4B illustrates process step 402. Process step 402 comprisesattaching electrodes to the glass base and the silicon piece. Oneelectrode forms the anode while the other electrode forms the cathode.The anode is attached to the silicon piece and the cathode is attachedto the glass base. The electrodes may comprise plates that fully contactthe glass base and silicon piece, points electrodes that make pointcontact with the glass base and silicon piece, and/or patteredelectrodes to provide patterned contact with the glass base and siliconpiece. For example, the patterned contact may focus bond creation atspecific locations on the glass base and silicon piece. The siliconpiece and glass base are heated to allow for anodic bonding. Forexample, the silicon piece and glass base may be heated to 250-400° C.The elevated temperature increases ion mobility within the glass base.The heating may be provided by an oven, hot plate, laser, and/or someother type of heat source. For example, heat can be applied by a laserand anodic bonding can be performing locally to the area heated by thelaser and the bond can be expanded as laser is moved. In some examples,pressure is applied to the glass base and the silicon piece to improvecontact at the bonding interface. For example, the electrodes mayadditionally comprise a mechanical clamp to apply the pressure.

When an adequate temperature has been reached (e.g., 300° C.), a voltagesource passes an electric current is passed between the anode and thecathode through the silicon piece and glass base. Typically, theelectric current is driven by an electric potential of several hundredvolts. In this example, the voltage source provides an electricpotential of 1000 volts. The electric current causes positively chargedions in the glass base like sodium (Na⁺) to diffuse towards the cathodeand causes negatively charged ions in the glass like oxygen (O⁻) todiffuse towards the silicon piece. The diffusion of the positivelycharged ions depletes the bonding surface of the glass base of positiveions allowing the bonding surface to develop a negative area charge. Theelectric current causes the silicon piece to develop a positive areachare at the bonding surface. The negatively charged ions pass out ofthe glass base at the bonding surface and react with the silicon pieceto create the anodic bond. For example, oxygen ions of the glass basemay pass out of the glass base and react with silicon atoms in thesilicon piece to form siloxane thereby hermetically bonding the glassbase to the silicon piece.

The temperature and voltage are maintained until an anodic bond isformed between the upper surface of the glass base and the lower surfaceof the silicon piece. Typically, the bonding process takes between 5-20minutes. Bonding time increases with a decrease in temperature. Bondingtime increases with a decrease in voltage. After the bond is formed, thesilicon piece and the glass base are cooled, and the electrodes areremoved. Once bonded, the upper surface of the glass base is exposedwhere the through hole in the silicon piece was drilled.

FIG. 4C illustrates process step 403. Process step 403 comprises placingthe silicon piece and glass base in an inert environment. For example,the silicon piece and glass base may be placed in a vacuum chamber wherea vacuum is drawn to create the inert environment. An alkali metal isdeposited through the through hole of the silicon piece onto the uppersurface of the glass base. The alkali metal may be deposited on theglass base using a nozzle. The nozzle may be lowered through the throughhole in the silicon piece and deposit the alkali metal. In someexamples, the exposed regions of the glass base may include indentationsto hold the alkali metal. The inert environment inhibits chemicalreaction in the alkali metal. The inert environment may comprise avacuum, a non-reactive gas, or some other type of medium that inhibitschemical reaction of the alkali metal. The alkali metal may comprise ametal like rubidium. In other example, the alkali metal may insteadcomprise a salt slush like a rubidium azide mixture.

Once the alkali metal is deposited in the through hole, the through holeis backfilled with inert gas like helium or nitrogen in addition to thealkali metal. Typically, the inert gas does not react, or reacts in onlya limited way, with the alkali metal deposits and alkali metal vapor. Aglass top is positioned on the upper surface of the silicon piece. Theglass top, glass base, and through hole walls of the silicon piececreate a cell cavity that fully enclose the alkali metal and thebackfilled inert gas. The backfilling creates a desired pressure withinthe cell cavity. For example, the pressure in the cell cavity may be setto allow a desired amount of the alkali metal to sublimate.

FIG. 4D illustrates process step 404. Process step 404 comprisesattaching an electrode to the glass top and the glass base. An electricpotential is generated by the voltage source to electrostatically clampthe glass top to the silicon piece. The electric potential induces acharge difference between the gas top and the silicon piece. The chargedifference secures the glass top to the silicon piece by electrostaticinteractions. In some examples, downward pressure is applied to theupper surface of the glass top and upward pressure is applied to thelower surface of the glass base to secure the glass top to the siliconpiece by other means. For example, the glass top may be mechanicallyclamped to the silicon piece. The mechanical clamp may be patterned toapply pressure to specific points on the glass top. For example, thepressure may be applied by pressure clamping. Pressure clampingcomprises increasing the atmospheric pressure in the environment aroundthe glass top, glass base, and silicon piece to secure the glass top tothe glass base.

Once the glass is secured to the silicon piece, a laser welding toolbonds the glass top to the upper surface of the silicon piece. Forexample, the laser welding tool may comprise a solid-state laser or agas laser. The laser welding tool applies high energy laser light to theglass top and the silicon piece. The laser light locally heats theinterface of the glass top and the silicon piece to a criticaltemperature(s) to create the laser bond. For example, the criticaltemperature may comprise a melting point and/or a glass transitionpoint. In this example, the heat provided by the laser light createsthree distinct bond types to form the laser bond. The first bond typecomprises a laser weld. At the critical temperature, the glass top andsilicon piece liquify at the bonding interface and melt into each otherto create the laser weld between the glass top and the upper surface ofthe silicon piece. The second bond type comprises a laser diffusionbond. The heat provided by the laser causes particle diffusion in theglass top and the silicon piece that hermetically joins the uppersurface of the silicon piece to the lower surface of the glass top. Thethird bond type comprises an anodic bond. The heat provided by the laserlight and the electric field provided by the electrostatic bindingcreates an anodic bond between the glass top and the silicon piece in amanner similar to that described in process step 402. The laser light ismoved around the through hole to create a laser bond that encircles thethrough hole. The laser welding tool removes the laser light and theglass top and silicon piece cool. The electrodes are removed from theglass top and the glass base. The interface between the glass top andsilicon piece where the laser light was applied solidifies to bind thelower surface of the glass top to the upper surface of the siliconpiece. The laser weld, laser diffusion bond, and the anodic bondhermetically bond the glass top and the silicon piece. In some examples,the heat generated by the laser initiates a chemical activation of thealkali metal. For example, the heat supplied by the laser light mayinitiate a desired chemical reaction in the alkali metal deposits tocreate the alkali metal vapor.

In other examples, when process step 404 utilizes a mechanical orpressure clamping method to secure the glass top to the glass base andthe electric potential is absent, an anodic bond is not formed duringlaser bonding and the laser bond only comprises the weld bond type andthe diffusion bond type. In such cases, once the laser bonding hascompleted, the glass top and silicon piece may be anodically bonded toreinforce the laser bond. By anodically bonding the glass top to thesilicon base after laser bonding is complete, the process can be doneoutside of the inert environment, the anodic bond reinforces the laserbond, and improves the hermeticity of the laser bonded glass-siliconvapor cell.

Advantageously, process 400 effectively and efficiently constructs laserbonded glass-silicon vapor cells. Moreover, the laser bonding processeffectively bonds the glass top to the silicon piece and locallyincreases the temperature of the laser bonded glass-silicon vapor cell.The locally elevated temperature inhibits undesired chemical reactionsfrom occurring that alter the chemical composition of the alkali vapor.Moreover, the locally elevated temperature effectively inhibits thediffusion of the alkali vapor into the glass top or the glass base. Theresulting lack of diffusion effectively maintains cell pressure andinhibits a change in the composition of the glass top and glass base.

FIG. 5 illustrates a top-down view of laser bonded glass-silicon vaporcells 500. Laser bonded glass-silicon vapor cells 500 comprise siliconwafer 501, laser welds 511, cell walls 512, cell cavities 513, andalkali salt slush 514. In this example, silicon wafer 501 is sandwichedbetween a glass base and glass top, however the glass base and glass topare omitted for the sake of clarity. Alkali salt slush 514 deposits arepositioned in cell cavities 513 on the surface of the glass base and arecontained by the glass base, glass top, and cell walls 512. The glasstop is bound to silicon wafer 501 by laser welds 511. The laser weldssurround cell walls 512 of the through holes hermetically sealing thecell cavities, however other patterns of laser welds may be used inother examples. The alkali deposits release alkali metal vapors thatfill cell cavities 513 created by the glass base, glass top, and cellwalls 512. The through holes in silicon wafer 501 may be drilledsimultaneously allowing for scalable manufacture of laser bondedglass-silicon vapor cells 500. Alkali salt slush deposits may bedeposited simultaneously with a patterned nozzle further allowing forscalable manufacture of laser bonded glass-silicon vapor cells 500.

FIG. 6 illustrates magnetoencephalography environment 600. Environment600 comprises target 601, headgear 611, sensors 621, cabling 631, andcontroller 641. Target 601 is depicted as a human brain but may compriseany magnetic field source. Headgear 611 houses sensors 621 and positionssensors 621 proximate to target 601. Headgear 611 may comprise a helmet,flexible cap, or some other type of headgear configured to hold sensors621. Sensors 621 comprise magnetometer devices configured to detectmagnetic fields generated by target 601 and transfer signalingcharacterizing the magnetic field. For example, sensors 621 may compriseOptically Pumped Magnetometers (OPMs). Sensors 621 comprise componentslike lasers, coils, laser bonded glass-silicon vapor cells, photodetectors, and heaters. Cabling 631 comprise sheathed metal wires thatcommunicatively couple sensors 621 to controller 641. Controller 641comprises a computing device configured to process sensor data receivedfrom sensors 621. Controller 641 comprises components like processors,memory, transceivers, bus circuitry, and the like. The memory storessoftware like operating systems, magnetic field modeling applications,modules, and the like. The processors retrieve and execute the softwarefrom the memory to drive the operation of controller 641.

FIG. 7 illustrates an exemplary operation of magnetoencephalographyenvironment 600. The structure and operation of environment 600 maydiffer in other examples. In some examples, target 601 is magneticallylinked to sensors 621. Sensors 621 are metallically linked to thecabling 631 which is metallically and detachably linked to controller641. Cabling 631 may comprise a ground shield that is coupled to theground in sensors 621 and to the ground in the in controller 641.Sensors 621 comprise probe lasers, pump lasers, one or more laser bondedglass-silicon vapor cells, photodetectors, coils, and heaters. The pumplaser and the probe laser may be combined, or additional lasers may beused. The laser bonded glass-silicon vapor cells comprise fully enclosedcavities that hold alkali metals and/or alkali metal vapors. The laserbonded glass-silicon vapor cells comprise an example of laser bondedglass-silicon vapor cells 100 and 500, however cells 100 and 500 maydiffer. Sensors 621 may include other electronics like flash circuitry,but they are omitted in this example.

Controller 641 comprises transceiver (XCVR) circuitry, processorcircuitry, and memory circuitry. The processor may comprise a FieldProgramable Gate Array (FPGA), an Application Specific IntegratedCircuit (ASIC), and the like. The memory may comprise flash circuitry,hard drives, and the like. The transceiver circuitry may comprise a pinand socket interface compatible with cabling 631. The processorcircuitry, memory circuitry, and transceiver circuitry communicate withone another using bus circuitry. Cabling 631 communicatively couplessensors 621 with controller 641. The processor in controller 641 maywrite and read sensor operational data to and from the memory. Theoperational data includes data like sensor ID, configuration parameters,and performance characteristics. For example, the operational data mayindicate the number of laser bonded glass-silicon vapor cells, therubidium level, pressure, build history, and notes for each of sensors621.

In operation, headgear 611 is secured to the head of target 601 tocontact sensors 621 with target 601. Cabling 631 couples to controller641. Controller 641 reads the memory to identify operational data forsensors 621. Controller 641 processes the operational data to generatecontrol signals for sensors 621. Controller 641 transfers the controlsignals to sensors 621 over cabling 631.

Sensors 621 operate in response to the control signals from controller641. Neuronal activity in target 601 generates electromagnetic wavesthat form a magnetic field. The laser bonded glass-silicon vapor cellsare positioned in the magnetic field. The cell cavities of the laserbonded glass-silicon vapor cells hold an alkali metal vapor likerubidium. In some examples, the cell cavities of the glass-silicon vaporcells contain other types of vapors like other alkali vapor types (e.g.,cesium), helium, nitrogen-vacancy centers, or vacuum encapsulations. Thedifferent types of laser bonded glass-silicon vapor cells could be usedinstead of, or along with, the alkali metal filled glass-silicon vaporcells in sensors 621. The laser bonded glass-silicon vapor cells areheated by the heaters. The pump laser emits a pump beam that iscircularly polarized at a resonant frequency of the vapor to polarizethe atoms of the alkali metal vapor. The probe laser emits a probe beamthat is linearly polarized at a non-resident frequency of the atoms toprobe the atoms of the alkali metal vapor. The probe beam enters thecell cavities of the laser bonded glass-silicon vapor cells wherequantum interactions with the atoms in the presence of the targetmagnetic field alter the energy/frequency of probe beam by amounts thatcorrelate to the magnetic field.

The photodetectors detect the probe beam after these alterations by thevapor atoms. The photodetectors generate and transfer correspondinganalog electronic signals that characterize the magnetic field. Forexample, the corresponding electronic signals may indicate the magneticfield strength at the location of the sensors 621. The photodetectorstransfer an electronic signal that carries the magnetic field data overcabling 631 to the controller 641. Controller 641 processes theelectronic signal to generate data that more fully characterizes themagnetic field. For example, the controller 641 may translate thesignals from sensors 621 into magnetic field strengths and tocharacterize the magnetic field. Controller 641 may process sensor datafrom multiple ones of sensors 621 to model the magnetic field in threedimensions. Controller 641 transfers the magnetic field characteristicsto downstream systems.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” As used herein, the terms “connected,”“coupled,” or any variant thereof means any connection or coupling,either direct or indirect, between two or more elements; the coupling orconnection between the elements can be physical, logical, or acombination thereof. Additionally, the words “herein,” “above,” “below,”and words of similar import, when used in this application, refer tothis application as a whole and not to any particular portions of thisapplication. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number, respectively. The word “or” in reference to alist of two or more items, covers all of the following interpretationsof the word: any of the items in the list, all of the items in the list,and any combination of the items in the list.

The phrases “in some embodiments,” “according to some embodiments,” “inthe embodiments shown,” “in other embodiments,” and the like generallymean the particular feature, structure, or characteristic following thephrase is included in at least one implementation of the presenttechnology and may be included in more than one implementation. Inaddition, such phrases do not necessarily refer to the same embodimentsor different embodiments.

The above Detailed Description of examples of the technology is notintended to be exhaustive or to limit the technology to the precise formdisclosed above. While specific examples for the technology aredescribed above for illustrative purposes, various equivalentmodifications are possible within the scope of the technology, as thoseskilled in the relevant art will recognize. For example, while processesor blocks are presented in a given order, alternative implementationsmay perform routines having steps, or employ systems having blocks, in adifferent order, and some processes or blocks may be deleted, moved,added, subdivided, combined, and/or modified to provide alternative orsubcombinations. Each of these processes or blocks may be implemented ina variety of different ways. Also, while processes or blocks are attimes shown as being performed in series, these processes or blocks mayinstead be performed or implemented in parallel or may be performed atdifferent times. Further any specific numbers noted herein are onlyexamples: alternative implementations may employ differing values orranges.

The teachings of the technology provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various examples described above can be combined to providefurther implementations of the technology. Some alternativeimplementations of the technology may include not only additionalelements to those implementations noted above, but also may includefewer elements.

These and other changes can be made to the technology in light of theabove Detailed Description. While the above description describescertain examples of the technology, and describes the best modecontemplated, no matter how detailed the above appears in text, thetechnology can be practiced in many ways. Details of the system may varyconsiderably in its specific implementation, while still beingencompassed by the technology disclosed herein. As noted above,particular terminology used when describing certain features or aspectsof the technology should not be taken to imply that the terminology isbeing redefined herein to be restricted to any specific characteristics,features, or aspects of the technology with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the technology to the specific examplesdisclosed in the specification, unless the above Detailed Descriptionsection explicitly defines such terms. Accordingly, the actual scope ofthe technology encompasses not only the disclosed examples, but also allequivalent ways of practicing or implementing the technology under theclaims.

To reduce the number of claims, certain aspects of the technology arepresented below in certain claim forms, but the applicant contemplatesthe various aspects of the technology in any number of claim forms. Forexample, while only one aspect of the technology is recited as a methodclaim, other aspects may likewise be embodied as an apparatus claim, orin other forms, such as being embodied in a means-plus-function claim.Any claims intended to be treated under 35 U.S.C. § 112(f) will beginwith the words “means for” but use of the term “for” in any othercontext is not intended to invoke treatment under 35 U.S.C. § 112(f).Accordingly, the applicant reserves the right to pursue additionalclaims after filing this application to pursue such additional claimforms, in either this application or in a continuing application.

What is claimed is:
 1. A laser bonded glass-silicon vapor cell forperforming atomic spectroscopy, the laser bonded glass-silicon vaporcell comprising: a glass base; a glass top; a silicon piece comprising athrough hole wherein a lower surface of the silicon piece ishermetically bonded to the glass base and an upper surface of thesilicon piece is laser bonded to the glass top; and a filling materialpositioned in a cavity formed by the through hole, the glass base, andthe glass top.
 2. The laser bonded glass-silicon vapor cell of claim 1wherein the filling material comprises an alkali metal.
 3. The laserbonded glass-silicon vapor cell of claim 1 wherein the filling materialcomprises a salt slush.
 4. The laser bonded glass-silicon vapor cell ofclaim 1 wherein the filling material comprises an inert gas.
 5. Thelaser bonded glass-silicon vapor cell of claim 1 wherein the fillingmaterial comprises a vacuum.
 6. The laser bonded glass-silicon vaporcell of claim 1 wherein the hermetic bond comprises an anodic bond. 7.The laser bonded glass-silicon vapor cell of claim 1 wherein thehermetic bond comprises another laser bond.
 8. The laser bondedglass-silicon vapor cell of claim 1 wherein the laser bond comprises alaser bond and an anodic bond.
 9. The laser bonded glass-silicon vaporcell of claim 1 wherein the through hole comprises an indentationconfigured to hold the filling material.
 10. The laser bondedglass-silicon vapor cell of claim 1 wherein the glass base and the glasstop comprise an anti-reflective coating.
 11. The laser bondedglass-silicon vapor cell of claim 1 wherein: the glass top comprises atleast one of a borosilicate glass or an aluminosilicate glass; and theglass base comprises at least one of a borosilicate glass or analuminosilicate glass.
 12. A method of manufacturing a laser bondedglass-silicon vapor cell for performing atomic spectroscopy, the methodof manufacture comprising: making a through hole in a silicon piece;hermetically bonding a lower surface of the silicon piece to a glassbase; positioning a filling material in the through hole of the siliconpiece on the glass base; clamping a glass top to the silicon piece tocontact the glass top with an upper surface of the silicon piece; laserbonding the upper surface of the silicon piece to the glass top; andremoving the clamping.
 13. The method of manufacturing of claim 12wherein the filling material comprises an alkali metal.
 14. The methodof manufacturing of claim 12 wherein the filling material comprises asalt slush.
 15. The method of manufacturing of claim 12 wherein thefilling material comprises an inert gas.
 16. The method of manufacturingof claim 12 wherein the filling material comprises a vacuum.
 17. Themethod of manufacturing of claim 12 wherein positioning the fillingmaterial in the through hole of the silicon piece on the glass base,clamping the glass top to the silicon piece to contact the glass topwith the upper surface of the silicon piece, and laser bonding the uppersurface of the silicon piece to the glass top comprises positioning thefilling material in the through hole of the silicon piece on the glassbase, clamping the glass top to the silicon piece to contact the glasstop with the upper surface of the silicon piece, and laser bonding theupper surface of the silicon piece to the glass top in an inertenvironment.
 18. The method of manufacturing of claim 12 whereinhermetically bonding the lower surface of the silicon piece to the glassbase comprises anodically bonding the lower surface of the silicon pieceto the glass base.
 19. The method of manufacturing of claim 12 furthercomprising anodically bonding the upper surface of the silicon piece tothe glass top.
 20. The method of manufacturing of claim 12 wherein:clamping the glass top to the silicon piece comprises applying anelectric current to the glass top and the silicon piece andelectrostatically binding the glass top to the silicon piece; andremoving the clamping comprises removing the electric current from theglass top and the silicon piece and electrostatically unbinding theglass top and the silicon piece.
 21. The method of manufacturing ofclaim 12 wherein laser bonding the silicon piece to the lower surface ofthe glass top further comprises chemically activating the fillingmaterial using heat generated by the laser bonding.